1. Field of the Invention
The present invention relates generally to spin valve sensors for magnetic heads, and more particularly to an improved free magnetic layer including CoFeCu for the spin valve sensor structure and a cap layers that includes oxides of zinc and tantalum.
2. Description of the Prior Art
Magnetic heads for hard disk drives typically have a read head portion including a magnetoresistive (MR) spin valve sensor structure for reading data from the disk of the hard disk drive. As is well known to those skilled in the art, such MR sensor structures include a plurality of thin film layers disposed between two magnetic shields that define the read gap. The thin film layers have particular magnetic properties, and are sensitive to the magnetic field of the data bits on the hard disk.
The thin film layers of a typical MR spin valve sensor will typically include at least one antiferromagnetic layer, at least one pinned magnetic layer, at least one free magnetic layer, and a cap layer. When reading data, a magnetic data bit of a hard disk will cause the direction of the magnetization of the free magnetic field layer to change, whereupon the electrical resistance of the sensor changes. This change in resistance (ΔR) affects the electrical current passing through the sensor, which is thus detected as a data signal.
Recently developed read heads may alternatively use a tunnel junction sensor, also known as a “tunnel valve”, abbreviated “TV”, for reading the magnetic data bit signals from the hard disk. The TV sensor typically includes a nonmagnetic tunneling barrier layer sandwiched between a pinned magnetic layer and a free magnetic layer. The tunnel junction sensor is itself typically sandwiched between first and second magnetic shield layers that also serve as first and second electrical lead layers, and are connected to the tunnel junction sensor for conducting a tunneling current through it. The TV sensor is configured to conduct Current Perpendicular to the Plane (CPP) of the film layers of the sensor, as opposed to an MR sensor as described above where the sense current is Current In the Plane (CIP) or parallel to film layers of the spin valve sensor.
The free layer material is preferably a magnetically soft material with low coercivity, which is a measure of the minimum field strength necessary to make changes in the orientation of the magnetization of the free layer. The free layer material necessarily must have this quality, as it is this layer's changes in magnetic alignment in response to the magnetic data bits of the hard disk that leads to changes in resistance, which is how the data is read. Currently the free layer is composed of a CoFe or NiFe layer, or is a bilayer structure of CoFe and NiFe layers. These materials may easily fall into multidomain magnetic states, where alignment of magnetic domains is not uniform. It is desirable however that the magnetization of the free layer be biased to be uniform throughout the entire layer. If the free layer material assumes a multidomain state, the read signal will be degraded.
In prior art magnetoresistive sensor structures a cap layer is typically deposited on top of the free magnetic layer, and the cap layer is typically composed of tantalum. The cap layer can influence the magnetoresistive properties of the sensor and an improved cap layer, such as is presented herein, enhances the performance of the sensor.